Implantable stimulation devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder sublaxation, etc. The description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227, which is hereby incorporated by reference in its entirety. However, the present invention may find applicability in many implantable medical device systems.
SCS is a well-accepted clinical method for reducing pain in certain populations of patients. As shown in FIGS. 1-2, an SCS system typically includes an Implantable Pulse Generator (IPG) 100, electrodes 106, at least one electrode lead (two such leads, 102a and 102b, are shown), and, optionally, at least one electrode lead extension 120. The electrodes 106, which reside on a distal end of the electrode leads 102a and 102b, are typically implanted along the dura 70 of the spinal cord, and the IPG 100 generates electrical pulses that are delivered through the electrodes 106 to nerve fibers within the spinal column 19. Individual electrodes 106 are arranged in a desired pattern and spacing to create an electrode array 110. Individual wires 112a-h within the electrode leads 102a and 102b connect with each electrode 106 in the array 110. The electrode leads 102a and 102b exit the spinal column and generally attach to one or more electrode lead extensions 120. The electrode lead extensions 120, in turn, are typically tunneled around the torso of the patient to a subcutaneous pocket where the IPG 100 is implanted. Alternatively, the electrode leads 102a and 102b may directly connect with the IPG 100.
In addition to precise placement of the electrode array in the dura 70, proper selection of the electrodes, i.e., which of the electrodes in the array should be active in a given patient, is critical for achieving effective stimulation therapy. However, because of the uncertainties of the distances of the electrodes from the neural target, the unknown nature of the specific conductive environment in which the electrode is placed, etc., the precise combination of active electrodes that will be perceived by a patient as providing optimal therapy generally cannot be known in advance. Moreover, the selected electrodes can be operated in many different modes (e.g., monopolar, bipolar, multipolar), and a given electrode can operate as a current source or sink with variable relative current amplitudes, pulse durations, and pulse frequencies, As a result, the patient may require that a different electrical stimulation therapy program be delivered through each lead, such that one stimulation therapy program is provided for the lead 102a implanted on the left side of the spinal column and a different stimulation therapy program is provided for the lead 102b implanted on the right side of the spinal column.
Determining these programs generally requires at the outset a “trial stimulation phase,” in which various electrode and stimulation parameters are tried and feedback is received from the patient as to which of the combinations feels most effective. During the trial stimulation phase, the patient's response to a variety of stimulation parameters may be analyzed over a period of time prior to complete implantation of the electrical stimulation system into the patient. A trial stimulation phase may last for several days, or even one or more weeks. During the trial stimulation phase, a patient is typically able to make adjustments to received stimulation. For example, a patient may be able to turn the stimulation on and off, or adjust one or more stimulation parameters, such as stimulation amplitude, or switch between two or more different pre-programmed stimulation patterns, as desired.
As is shown in FIGS. 3 and 4, during the trial stimulation phase, the distal end of leads 102a and 102b are implanted into the patient at the selected location, while the proximal end of the leads are electrically coupled to an external trial stimulator (ETS) 140 via external cable box assemblies 142 (and, optionally, one or more trial stimulation cable extensions 132). Each external cable box assembly 142 consists of external cable box 150, trial stimulation cable 134, and male connector 135. As its name implies, the ETS 140 is external to (i.e., not implanted in) the patient. The ETS 140 generally mimics operation of the IPG 100, which at this point is not yet implanted, and allows different stimulation programs to be established for each lead 102a and 102b. Once these programs are determined, the IPG 100 may then be implanted, the determined programs written into the IPG 100, and the leads 102a and 102b coupled to the IPG for a completed implanted stimulation solution.
Because the trial stimulation phase may last up to several weeks, it is possible that the trial stimulation cables 134 (or their extensions 132) may become unplugged from the ETS 140. In the case of ETSs with multiple ports 141, if two or more external cable box assemblies 142a and 142b appear identical to the user, then the user may re-connect the trial stimulation cables 134a and 134b into different ports 141a and 141b on the ETS 140 than they were plugged into when the patient was designing the proper electrical stimulation therapy. This would result in, e.g., the stimulation therapy program designed for the right side of the patient's spinal column being delivered to the left side of the patient's spinal column and vice versa, thus potentially delivering undesired stimulation to the patient.
Presently, labels, implemented as stickers, are typically used to identify the proper connection of each external stimulation cable 134 to the appropriate port 141 on the ETS 140. However, these labels can become loose and fall off or can be confusing to some patients. Also, there is no failsafe in place in the system should the patient fail to or refuse to re-plug in the external stimulation cables 134 correctly.
Given these shortcomings, the art of implantable medical devices would benefit from an improved electronic, low-cost method for assuring the proper connection of external cables to an external trial stimulator, and this disclosure presents such a solution.